Because of the need to conserve oil resources, a great deal of interest and effort have been directed to the development of fuel slurries in which coal of appropriate particulate size replaces some of the oil, as in coal-oil and coal-oil-water slurries, or all of the oil, as in coal-water slurries, for industrial use such as utilities. As in the case of oil, such fuel slurries are fed into the fuel combustion chamber, e.g. furnace or boiler, through an atomizing device which breaks up the slurry fuel into a fine particulate spray. Such atomizing devices have small orifices that can become clogged by any excessively sized coal particles which may be present in the fuel, thereby interrupting the combustion process and requiring clearing of the atomizer.
This invention relates to coal-liquid slurries which have been fully processed for direct use as a fuel, as distinguished, for example, from a slurry designed primarily for long distance pipeline transport, which may require additional processing, such as change in coal concentration, coal particle sizes, additives to increase stability, etc., for final use as a fuel. The term "slurry fuel" or "fuel slurry" as employed in this specification and claims, is to be construed in accordance with the foregoing definition.
The fine coal particles in slurry fuels properly formulated for efficient combustion are within a particle size range which readily burns in the combustion chamber. Atomizing devices for spraying the slurry into the combustion chamber are generally designed with small orifices of adequate diameter to accomodate the largest particle sizes in the fuel slurry formulation. However, after final formulation of the fuel slurries, excessively-sized coal particles in the form of agglomerates may contaminate the slurry. These may be aggregates of dried slurry which have formed on storage tank or pipe walls, aggregates resulting from exposure to air drying by evaporation at the surface of stored fuel or during handling, or aggregates which may form within the slurry during extended storage periods. The slurries may also include some excessively sized primary particles which occur accidentally during formulation of the fuel slurry.
The object of this invention is to provide a means for eliminating excessively sized contaminant coal particles, in the form of agglomerates or accidental primary particles, which may be present in the slurry fuel prior to entry of the fuel into the slurry atomizer and, thereby to prevent costly clogging of the atomizing device.